It is well known that in the processing of photographic light sensitive materials the processing solution has to be made up with fresh solution known as replenisher solution and that it is necessary to remove used processing solution either periodically or continuously from the tank in which it is held. This is usually carried out by causing the addition of the replenisher solution to displace processing solution from its tank. This displaced processing solution may then be discarded or, more commonly, treated in some way to recover components of value.
For example U.S. Pat. No. 3,418,913 discloses a processor having a plurality of tanks for holding processing solutions, including a developer solution and a fixer solution followed by a tank for water for washing the photographic material. The processing solutions in the tanks are recirculated by withdrawing the solution through a filter located within the tank and then pumping the solution through a heat exchanger and back to the tank. Replenishment solutions are provided through a replenishment line or conduit under the control of solenoid operated valves. The replenishment solution is provided downstream from the outlet of the tank and before the solutions reach the pump so that the replenishment solution is mixed with solution from the tank and cooled prior to being delivered to the tank with previously used solution.
U.S. Pat. No. 5,353,085 discloses an automatic processing system which includes replenishment with a concentrated solution and in which used processing solution is treated by a series of steps including evaporation and electro-dialysis.
Further U.S. Pat. No. 5,184,165 also describes an automatic processing system which eliminates the need for manual mixing of the processing solutions.